An important tool in circuit board design is the ability to easily and accurately locate and measure electromagnetic emissions from an operating circuit board. The prior art electronic emission monitors are represented by Canadian Letters Patent 1,286,724 assigned to Northern Telecom Limited, granted on Jul. 23, 1991; U.S. Pat. No. 4,829,238 granted on May 9, 1989; U.S. Pat. No. 5,006,788 granted on Apr. 9, 1991; and, U.S. Pat. No. 5,218,294. These patents describe a method and apparatus for monitoring electromagnetic emission levels from operating printed circuit boards.
The prior art enabled the user to carry out two types of scans: spectral, that is, signal strength relative to the frequency of the scanner, and spatial, that is, signal strength relative to the position of the signal on the printed circuit board. The spectral scan retains only the highest value observed at each frequency point, regardless of the probe, and the display is, therefore, merely a profile of peak electromagnetic amplitudes plotted against frequency. All other readings are discarded. A spatial scan takes a reading of the signal level at the designated frequency, for each probe within the selected scan area. The scan results are retained in a display file which provides a color coded map of the current flows (signal strength) in the scan area at the defined frequency. The amount of time required to complete the scan is in the range of 95 seconds.
The disadvantages and limitations associated with the prior art apparatus relate to the fact that it cannot scan the board under test fast enough for use in production line testing. To be effective in such an application requires an method and apparatus for gathering spectral information from all locations of the printed circuit board under test in much less than one second.